Laser cutting and removal of contoured shapes from transparent substrates

ABSTRACT

A method for cutting, separating and removing interior contoured shapes in thin substrates, particularly glass substrates. The method involves the utilization of an ultra-short pulse laser to form defect lines in the substrate that may be followed by use of a second laser beam to promote isolation of the part defined by the interior contour.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/097,999 filed on Oct. 31, 2018, which claims the benefit of priorityunder 35 U.S.C. § 371 of International Application No.PCT/US2017/031030, filed on May 4, 2017, which claims the benefit ofpriority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No.62/350,978 filed on Jun. 16, 2016 and U.S. Provisional Application Ser.No. 62/332,618 filed on May 6, 2016, the contents of which are reliedupon and incorporated herein by reference in their entirety as if fullyset forth below.

FIELD

The present disclosure relates generally to apparatus and methods forcutting transparent substrates, and more particularly to apparatus andmethods for cutting and removing interior portions from a glass sheet.

BACKGROUND

The cutting of articles from thin substrates of transparent materials,such as glass, can be accomplished by focused laser beams that ablatesubstrate material along a predetermined contour, where multiple passesare used to remove layer after layer of material until a part defined bythe contour is no longer attached to the outer substrate piece. Theproblem with such ablative processes is that they require many passes ofthe laser beam to remove the material layer-by-layer, they generatesignificant debris that can contaminate the major surfaces of thearticle, and they can generate significant subsurface damage along theseparated edge surfaces of the article as well as surface contamination.This damage may require extensive grinding or polishing to remove,adding to the complexity of the manufacturing process and increasingmanufacturing cost. Such damage can also be particularly detrimental toprocesses for the manufacture of articles requiring defect-free edgesand surfaces, for example, glass platters for hard disc drives (HDD),digital encoders, display devices e.g., display panels or display coverglass and the like.

SUMMARY

Embodiments described herein relate to a non-ablative process forcutting articles from thin transparent substrates (e.g., equal to orless than about 10 millimeters, for example in a range from about 0.01millimeters to about 10 millimeters, in a range from about 0.05millimeters to about 5 millimeters, in a range from about 0.05 to about1 millimeters, or in a range from about 0.05 millimeters to about 0.7millimeters) comprising glass, glass ceramic, ceramic or selectedminerals, such as sapphire.

The cutting is based on inducing nonlinear absorption in the material tobe processed by directing a laser beam of sufficient intensity at thesubstrate, wherein the substrate would be substantially transparent tothe laser beam at a lesser intensity. Preferably, the laser beam is apulsed laser beam. The cutting comprises producing a linear focus linewithin the transparent substrate that produces damage along the focusline, thereby creating a defect line. Unlike laser filamentationprocesses that rely on self-focusing as a result of the Kerr effect, inembodiments described herein, the laser and associated optics produce aline focus that does not depend on the presence of the substrate.Methods according to the present disclosure generate an inducedabsorption within the substrate along the line focus that produces adefect within the substrate along the laser beam focal line, preferablythrough an entire thickness of the substrate, without laserfilamentation. The resulting defect may contain pockets or voids, but istypically not a through hole extending unobstructed through the entirethickness of the substrate.

Accordingly, a method of cutting an article from a substrate isdisclosed, comprising: focusing a pulsed laser beam into a laser beamfocal line, the laser beam focal line extending substantially orthogonalto a major surface of the substrate; directing the laser beam focal lineinto the substrate at a first plurality of locations along a firstpredetermined path, the laser beam focal line generating an inducedabsorption within the substrate that produces a defect line within thesubstrate along the laser beam focal line at each location of the firstplurality of locations, wherein the first predetermined path is a closedpath; heating the substrate along the first predetermined path topropagate a crack through each defect line of the first plurality oflocations, thereby isolating an interior plug from the substrate; andheating the interior plug after the isolating to remove the plug fromthe substrate. The substrate is transparent at a wavelength of thepulsed laser beam. The first predetermined path may, for example, be acircular path. The substrate may comprise glass, glass ceramic, ceramicor sapphire.

In some embodiments, the defect line extends through an entire thicknessof the substrate.

In some embodiments, a plurality of substrates may be stacked, forexample two substrate, three substrates or more substrates, wherein thelaser beam focal line extends through each substrate of the stack ofsubstrates, thereby forming a defect line that extends through eachsubstrate of the stack of substrates.

The method may further comprise directing the laser beam focal line intothe substrate at a second plurality of locations along a secondpredetermined path not intersecting the first predetermined path, thelaser beam focal line generating an induced absorption within thesubstrate that produces a defect line along the laser beam focal linewithin the substrate at each location of the second plurality oflocations.

The method may further comprise heating the substrate along the secondpredetermined path to propagate a crack through each defect line of thesecond plurality of locations. The second predetermined path may, forexample, be a circular path concentric with the first predeterminedcircular path. A radius of the second predetermined path can be greaterthan a radius of the first predetermined path such that the firstpredetermined path and the second predetermined path defining an annulustherebetween.

The method may further comprise directing the laser beam focal line intothe substrate at a third plurality of locations along a thirdpredetermined path, the laser beam focal line generating an inducedabsorption within the substrate that produces a defect line along thelaser beam focal line within the substrate at each location of the thirdplurality of locations, the third predetermined path extending from anedge of the substrate to the second predetermined path.

The method may further comprise heating the substrate along the thirdpredetermined path to propagate a crack through each defect line of thesecond plurality of locations. Heating the substrate along the firstpredetermined path may comprise traversing a second laser beam, forexample a defocused laser beam, over the first predetermined path. Thesecond laser beam may be a continuous wave laser beam. The second laserbeam may be a CO₂ laser beam or a CO laser beam, e.g., a continuous waveCO₂ laser or a continuous wave CO laser.

Heating the plug after the isolating may comprise heating the plug witha heat source selected from the group consisting of a third laser beam,an infrared LED, an infrared lamp, and an electrical resistance heater.The third laser beam may be generated from the same laser as the secondlaser beam. The heat source may heat only a central area of the plug.

The third laser beam may traverse on the plug a plurality of closedpaths spaced apart from the first predetermined path. The plug candeform during heating of the plug. In some embodiments, the plug mayfall from the substrate without application of an externally appliedforce during or after heating the plug.

At least a portion of the plug may be heated to a temperature equal toor greater than a softening temperature of the substrate.

The method may further comprise positioning the substrate on a firstmajor surface of a support substrate, the first major surface of thesupport substrate comprising a recess positioned below the plug.

The substrate may be restrained on the support substrate to preventmovement of the substrate. For example, in some embodiments, the supportsubstrate may comprise a plurality of passages extending from a firstmajor surface of the support substrate to a second major surface of thesupport substrate, and wherein the restraining comprises applying avacuum to the plurality of passages.

The recess may further comprise a passage extending from the recess to asecond major surface of the support substrate, wherein the methodfurther comprising reducing a pressure within the recess through apassage extending from a floor of the recess to the second major surfacethrough which a vacuum can be applied. A depth of the recess may begreater than a thickness of the plug.

The method may further comprise cooling the interior plug after theheating of the plug. In some embodiments, the interior plug drops fromthe substrate upon cooling without application of an external mechanicalforce to the interior plug.

In another embodiment, a glass article made by any of the foregoingaspects is described.

In still another embodiment, a method of cutting an article from asubstrate is disclosed, comprising: focusing a pulsed laser beam into alaser beam focal line, the laser beam focal line extending substantiallyorthogonal to a major surface of the substrate; directing the laser beamfocal line into the substrate at a first plurality of locations along afirst predetermined path, the laser beam focal line generating aninduced absorption within the substrate that produces a defect linewithin the substrate along the laser beam focal line at each location ofthe first plurality of locations, wherein the first predetermined pathis a closed path; heating the substrate along the first predeterminedpath to propagate a crack through each defect line of the firstplurality of locations, thereby isolating an interior plug from thesubstrate; and cooling the interior plug after the isolating to removethe plug from the substrate.

In some embodiments, a plurality of substrates may be stacked, forexample two substrate, three substrates or more substrates, wherein thelaser beam focal line extends through each substrate of the stack ofsubstrates, for example an entire thickness of the stack, therebyforming a defect line that extends through each substrate of the stackof substrates.

The method may further comprise heating the plug prior to the cooling.

Heating the plug may comprise directing a second laser beam at a centralregion of the plug. The second laser beam may be, for example, a CO₂laser beam or a CO laser beam.

Heating the plug may comprise heating at least a portion of the plug toa temperature equal to or greater than a softening temperature of thesubstrate.

In some embodiments, cooling the plug may comprise directing a coolingfluid, for example liquid nitrogen, against the plug.

In some embodiments, heating the plug may comprise heating the entiresubstrate.

In yet another embodiment, a glass article is described, comprising: afirst major surface; a second major surface opposite the first majorsurface; a circular inner perimeter; a circular outer perimeterconcentric with the inner perimeter, the inner perimeter and the outerperimeter defining an annulus therebetween, a thickness extendingbetween the first and second major surfaces equal to or less than about1 millimeter, a first edge surface between the first and second majorsurfaces and extending around the inner perimeter and a second edgesurface between the first and second major surfaces and extending aroundthe outer perimeter, at least one of the first or second edge surfacescomprising a plurality of defect lines extending orthogonally betweenthe first and second major surfaces; and wherein a diameter of eachdefect line is less than or equal to about 5 micrometers. The first andsecond major surfaces may be free of any coating. The first and secondmajor surfaces may be unground and unpolished. The first and second edgesurfaces may be unground and unpolished.

In still another embodiment, a glass article is disclosed, comprising: afirst major surface; a second major surface opposite the first majorsurface; a circular inner perimeter; a circular outer perimeterconcentric with the inner perimeter, the inner perimeter and the outerperimeter defining an annulus therebetween, a thickness extendingbetween first and second major surfaces equal to or less than about 1millimeter, a first unground and unpolished edge surface between thefirst and second major surfaces and extending around the inner perimeterand a second unground and unpolished edge surface between the first andsecond major surfaces and extending around the outer perimeter; andwherein an R_(a) surface roughness of at least one of the first orsecond edge surfaces is equal to or less than about 0.5 micrometers.

At least one of the first or second edge surfaces may comprise aplurality of defect lines extending orthogonally between the first andsecond major surfaces, and wherein a diameter of each defect line isless than or equal to about 5 micrometers.

A depth of subsurface damage along either one of the first or secondedge surfaces may be equal to or less than about 75 micrometers, forexample equal to or less than about 25 micrometers. A warp of the glassarticle can be equal to or less than about 50 micrometers, for example,equal to or less than about 15 micrometers.

An anneal point of the glass article may be equal to or greater thanabout 700° C., for example equal to or greater than about 800° C.

A compaction of the glass article after exposure to a temperature of600° C. for a period of 30 minutes, upon cooling to a temperature of 23°C., can be equal to or less than about 35 ppm, for example equal to orless than about 20 ppm.

The glass article may comprise equal to or less than about 5 MPainternal residual stress.

In some embodiments, the glass article may be a chemically strengthenedglass, for example a ion-exchanged glass.

An average roughness R_(a) of either one of the first or second majorsurfaces can be equal to or less than about 1 nanometer, for exampleequal to or less than about 0.5 nanometers.

The glass article may comprise equal to or less than about 0.5 wt. %.SnO₂, for example equal to or less than about 0.15 wt. % SnO₂.

A distance between adjacent defect lines of the plurality of defectlines may be equal to or less than about 7 micrometers, for exampleequal to or less than about 5 micrometers, for example equal to or lessthan about 3 micrometers, for example equal to or less than about 1micrometer.

The glass article may comprise less than or equal to 0.1% of an alkalimetal oxide.

In some embodiments, the first and second major surfaces may be ungroundand unpolished. The first and second major surfaces may be free of anycoating.

In some embodiments, a diameter of the circular outer perimeter iswithin +/−15 micrometers of a predetermined nominal circular outerdiameter, for example within +/−10 micrometers of the predeterminednominal circular outer diameter

In some embodiments, a diameter of the circular inner perimeter iswithin +/−25 micrometers of a predetermined nominal circular innerdiameter, for example within +/−10 micrometers of the predeterminednominal circular inner diameter

In some embodiments, a center of the inner circular perimeter and acenter of the outer circular perimeter are displaced from each other byno more than about 10 micrometers, for example by no more than about 5micrometers

In yet another embodiment, a method of cutting a glass article from atransparent glass substrate is described, comprising: forming a firstplurality of defects along a first closed path, the first plurality ofdefects extending into the glass substrate from a first major surface toan opposing major surface orthogonal to the first and second majorsurfaces; propagating a crack through each defect of the first pluralityof defects, thereby isolating a plug from the substrate; heating theplug after the isolating; and wherein the plug falls from the substrateafter a cessation of the heating without the application of an externalforce.

The method may further comprise forming a second plurality of defectsalong a second closed path concentric with the first closed path, thesecond plurality of defects extending into the glass substrate from thefirst major surface to the opposing major surface orthogonal to thefirst and second major surfaces, wherein a radius of the second closedpath is greater than a radius of the first closed path.

The method may further comprise forming a third plurality of defectsalong a third path from an edge of the glass substrate to the secondclosed path, the third plurality of defects extending into the glasssubstrate from the first major surface to the opposing major surfaceorthogonal to the first and second major surfaces.

In some embodiments, a plurality of substrates may be stacked, forexample two substrate, three substrates or more substrates, wherein thelaser beam focal line extends through each substrate of the stack ofsubstrates, thereby forming a defect line that extends through eachsubstrate of the stack of substrates.

The method may further comprise heating the glass substrate along thesecond closed path, thereby driving a crack along the second closedpath.

The method may further comprise heating the glass substrate along thethird path, thereby driving a crack along the third path.

In still another embodiment, a method of cutting a glass article from aglass substrate is disclosed, comprising: forming a first plurality ofdefects along a first closed path, the first plurality of defectsextending into the glass substrate from a first major surface to anopposing second major surface, the plurality of defect lines orthogonalto the first and second major surfaces; propagating a crack through eachdefect line of the first plurality of defect lines, thereby isolating aplug from the substrate; heating the plug after the isolating; andwherein the plug falls from the substrate after a cessation of theheating.

In some embodiments, a plurality of substrates may be stacked, forexample two substrate, three substrates or more substrates, wherein thelaser beam focal line extends through each substrate of the stack ofsubstrates, thereby forming a defect line that extends through eachsubstrate of the stack of substrates.

The method may further comprise positioning the glass substrate on asupport substrate, the support substrate comprising a recess positionedbeneath the first closed path, wherein a radius of the recess is greaterthan a radius of the first closed path.

The method may further comprise applying a vacuum to the recess duringor after the heating.

In some embodiments, the forming comprises focusing a pulsed first laserbeam into a laser beam focal line, the laser beam focal line extendingsubstantially orthogonal through an entire thickness of the glasssubstrate between the first and second major surfaces of the glasssubstrate, the laser beam focal line generating an induced absorptionwithin the substrate that produces a defect within the substrate alongthe laser beam focal line.

In some embodiments, propagating a crack may comprise heating the glasssubstrate along or adjacent to the first closed path with a secondlaser. The second laser may be, for example, a CO₂ or a CO laser.

In still another embodiment, a glass article is described, comprising: aglass sheet including a first major surface, a second major surfaceopposing and substantially parallel to the first major surface, and athickness between the first and second major surfaces; a first pluralityof circular fault lines, each circular fault line of the first pluralityof fault lines comprising a plurality of defect lines extending throughthe thickness of the glass sheet and orthogonal to the first and secondmajor surfaces, the plurality of defect lines of each circular faultline of the first plurality of circular fault lines spaced apart by adistance in a range from about 2 micrometer to about 20 micrometers,each circular fault line of the first plurality of circular fault linesincluding a center; and wherein the center of each circular fault lineof the first plurality of circular fault lines is displaced from anadjacent circular fault line of the first plurality of circular faultlines.

The glass sheet may further comprise a second plurality of circularfault lines, each circular fault line of the second plurality of faultlines comprising a plurality of defect lines extending through thethickness of the glass sheet and orthogonal to the first and secondmajor surfaces, the defect lines of each circular fault line of thesecond plurality of circular fault lines spaced apart by a distance in arange from about 2 micrometer to about 20 micrometers; and wherein eachcircular fault line of the first plurality of circular fault lines iscircumscribed by a circular fault line of the second plurality ofcircular fault lines.

In some embodiments, each circular fault line of the first plurality ofcircular fault lines is an inner fault line and each circular fault lineof the second plurality of fault lines is an outer fault line, eachouter fault line of the second plurality of circular fault linesconcentric with a respective inner fault line of the first plurality ofcircular fault lines.

The glass sheet comprises a length L and a width W orthogonal to L, eachouter fault line defining a disc with a radius r, and in someembodiments ((L·W)−nπr²)/(L·W) is greater than 0.66, where n representsa total number of discs defined on the glass sheet. In some embodiments,L·W is greater than 671,600 mm² and n is equal to or greater than 70.

The thickness of the glass sheet may be in a range from about 50micrometers to about 3 millimeters, for example in a range from about0.6 millimeters to about 0.7 millimeters.

In some embodiments, the first and second major surfaces of the glasssheet may be unground and unpolished.

In yet another embodiment, a method of cutting a glass article from aglass substrate is disclosed, comprising: forming a first plurality ofdefect lines along a first closed path, the first plurality of defectlines extending into the glass substrate from a first major surface toan opposing second major surface, the plurality of defect linesorthogonal to the first and second major surfaces; propagating a crackthrough each defect of the first plurality of defects, thereby isolatinga plug from the substrate, the plug comprising a first major surfacedefined within a first outer perimeter, a second major surface definedwithin a second outer perimeter and a thickness P_(thickness) extendingbetween the first and second major surfaces, and an edge surfaceextending between the first and second major surfaces, wherein anintersection of the edge surface and the first major surface defines afirst edge and an intersection of the edge surface and the second majorsurface defines a second edge; and changing a temperature of the plugand/or the glass substrate such that, D_(initial)>Sqrt(D_(final)²+P_(thickness) ²), wherein D_(initial) represents an initial diameterof the plug, D_(final) represents a final diameter of the plug afterchanging the temperature.

In some embodiments, a plurality of substrates may be stacked, forexample two substrates, three substrates or more substrates, wherein theplurality of defect lines extend through each substrate of the stack ofsubstrates.

In some embodiments, changing the temperature may comprise heating theentire substrate, then cooling the plug with a coolant.

In some embodiments, changing the temperature may comprise cooling theplug with a coolant.

Additional features and advantages of the embodiments disclosed hereinwill be set forth in the detailed description that follows, and in partwill be readily apparent to those skilled in the art from thatdescription or recognized by practicing the embodiments describedherein, including the detailed description that follows, the claims, aswell as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments intended toprovide an overview or framework for understanding the nature andcharacter of the disclosure. The accompanying drawings are included toprovide further understanding, and are incorporated into and constitutea part of this specification. The drawings illustrate variousembodiments of the disclosure, and together with the description serveto explain the principles and operations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments included herein, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present disclosure.

FIG. 1 is an illustration of an article including both outer and innercontours to be cut from a starting parent substrate, the outer contourcircumscribing the article and the inner contour circumscribing a plugto be removed from the article;

FIG. 2 is a schematic diagram showing an exemplary optical arrangementto produce a focal line within a substrate;

FIG. 3 is a scanning electron microscope image showing a top view of adefect line formed in a glass substrate, illustrating an initial holeand a rim about the hole with ejecta evident;

FIG. 4 is a scanning electron microscope image that is a cross sectionalview of a glass substrate showing several defect lines formed in a glasssubstrate;

FIG. 5 is a schematic diagram of a substrate positioned on a substratesupport, wherein one or more lasers are used to create defect lines, andsubsequent fault lines, in a substrate;

FIG. 6 is a top view of a substrate comprising a plurality of faultlines defining a plurality of parts to be removed from the substrate;

FIG. 7 is a top view of a substrate showing a plurality of defect linesformed along a path;

FIG. 8 is a schematic diagram showing a crack extending into a part tobe removed from the substrate;

FIGS. 9A-9D are schematic diagrams of difference scenarios resultingfrom the order in which separation along a fault line occurs;

FIG. 10 is a cross sectional diagram showing a laser being used to drivea crack along a fault line;

FIG. 11 is a cross sectional view of the glass substrate of FIG. 8positioned on a support substrate, wherein a portion of the plugs formedin the glass substrate are heated to a temperature at or greater thanthe softening temperature of the plug;

FIG. 12 is a cross sectional view of the glass substrate of FIG. 11positioned on a support substrate, wherein a vacuum is applied to theisolated plugs through recesses in the support substrate, therebycausing air pressure above the plugs to drive the plugs from the glasssubstrate;

FIG. 13 illustrate a more densely packed arrangement of parts on asubstrate (e.g., hexagonal close-packed);

FIG. 14A is a graph showing warp of the original warp of a substratefrom which an annulus is produced; and

FIG. 14B is a graph showing warp of the annulus produced from thesubstrate of FIG. 14A.

DETAILED DESCRIPTION

Disclosed herein is a process for cutting and removing one or morearticles from a thin substrate of brittle material, for example a thintransparent material. The material may be, for example, a transparentglass material, a transparent glass ceramic material or a transparentceramic material. The process is particularly useful for cutting andremoving interior contoured shapes from thin substrates of transparentglass. The method utilizes an ultra-short duration pulsed laser beam andaccompanying optics to form defects in the substrate along a focus linein the substrate. The focus line, and the resultant defect line, mayextend through the entire thickness of the substrate, although infurther embodiments the focus line and the resultant defect line mayextend through only a portion of the thickness of the substrate. Aplurality of defect lines may be formed along a predetermined path,thereby forming a fault line. The predetermined path may be a closedpath such that the predetermined path circumscribes the part to beremoved, although in further embodiments the predetermined path may notbe a closed path. In some embodiments, formation of the fault line maybe followed by use of a laser beam, for example a CO₂ laser beam, thatis traversed along the path to promote full separation (isolation) ofthe part along the fault line by heating the substrate along the faultline. The laser process described below can generate full body cuts in avariety of glasses, with low sub-surface damage (extending less thanabout 75 micrometers), and excellent surface average roughness (whereinan average surface roughness R_(a) of the cleaved edge surface is equalto or less than about 0.5 micrometers). Average surface roughness is aquantitative calculation of the relative roughness of a linear profileor area, expressed as a single numeric parameter (R_(a)). Averagesurface roughness can be measured, for example, using an opticalprofilometer (e.g., white light or laser interferometry), or by contactmethods (typically employing a diamond stylus). Suitable instruments areavailable, for example, from Zygo® and Nikon.

As used herein, sub-surface damage (SSD) is defined as the extent ofcracks or “checks” perpendicular to the cut edge of the substrate. Insome embodiments, depending on substrate type, separation of thesubstrate may be accomplished in a single pass of the pulsed laser. Themagnitude of the distance these cracks extend into the substrate candetermine the amount of material removal that may later be needed fromgrinding and polishing operations to remove edge defects and improveedge strength. SSD may be measured using, for example, a confocalmicroscope or a fluorescing die to observe light scattering from anycracks that may be present, and determining the maximum distance thecracks extend into the body of the substrate and/or article over a givencut edge. Alternatively, the exposed edge may be polished iterativelywhile examining the edge using a confocal microscope. As material ispolished off, the amount of cracks evident decreases. Eventually, whenall the defects are gone, the depth of material removed is reported asthe sub-surface damage.

Although the following description is presented in respect of glasssubstrates, e.g., glass sheets, it should be recognized that embodimentsof the present disclosure can be applicable to a range of transparentmaterials, for example glass, glass ceramic, ceramic or selectedminerals (e.g., sapphire).

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular value tothe other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another embodiment. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

Directional terms as may be used herein—for example up, down, right,left, front, back, top, bottom—are made only with reference to thefigures as drawn and are not intended to imply absolute orientation.

Unless otherwise expressly stated, it is not intended that any methodset forth herein be construed as requiring that its steps be performedin a specific order, nor that with any apparatus, specific orientationsbe required. Accordingly, where a method claim does not actually recitean order to be followed by its steps, or that any apparatus claim doesnot actually recite an order or orientation to individual components, orit is not otherwise specifically stated in the claims or descriptionthat the steps are to be limited to a specific order, or that a specificorder or orientation to components of an apparatus is not recited, it isnot intended that an order or orientation be inferred, in any respect.This holds for any possible non-express basis for interpretation,including: matters of logic with respect to arrangement of steps,operational flow, order of components, or orientation of components;plain meaning derived from grammatical organization or punctuation, andthe number or type of embodiments described in the specification.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a” component includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

As used herein, transparent means the incident laser beam used to formdefect lines loses no more than 10% of the impinging energy permillimeter of distance propagated within the substrate in the linearabsorption regime.

As used herein, the term defect refers to cracks, including microcracks,and other bond-breaking damage to the molecular structure of asubstrate. Defects may include mechanical damage, such as by contact ofthe substrate to mechanical objects, or the damage may be the result ofinteraction of the material with electromagnetic fields, such as a laserbeam.

As used herein, a defect line refers to a linear defect (a single longdefect or a series of defects arrayed in a line), typically, althoughnot exclusively, extending in a thickness direction of the substrate(orthogonal to the major surfaces of the substrate).

As used herein, a contour or path refers to a virtual two dimensionalshape on a substrate. Thus, while a path itself is a virtual shape, thepath may be approximated, for example, by a fault line or a crack. Aclosed path is a path that forms a continuous loop, the loopcircumscribing and bounding an interior area. A path may be followed,for example, by a laser beam impinging on the surface of the substrate.

As used herein, a fault line refers to a series of closely spaced defectlines positioned along a path. Similarly, a release line is a fault linetypically extending from an edge of the substrate to a fault linedefining an interior shape, or between two fault lines defining interiorshapes. Accordingly, while release lines are fault lines, as used hereinthe term fault line will be used to describe shapes internal to theglass substrate (not intersecting an edge of the substrate), whereasrelease lines will denote fault lines extending from an edge of thesubstrate to an interior fault line, or from one interior fault line toanother interior fault line.

As used herein, the term separation refers to a disruption in a material(e.g., damage), such as a crack or other defect (generically, a cleave),that forms two opposing surfaces. Separation, then, should beinterpreted as cleaving that does not result in the complete isolationof one portion of the substrate bounded by the cleave from another,adjacent portion of the substrate. In contrast, isolation refers to acleave that extends completely through the substrate along apredetermined path that results in complete isolation of a first portionof the substrate bounded by the cleave from another portion of thesubstrate adjacent to the first portion such that the first portion isindependently movable relative to the adjacent portion. A cleave thatresults in isolation, for example, may extend completely around a closedpath (i.e., a closed contour) in a substrate and further extendingcompletely through the thickness of the substrate. Such a cleave definesan interior portion of the material completely isolated from a portionof the material outside the closed path, such that the inner portion iscapable of motion independent of the surrounding portion outer. Itshould be noted, however, that isolation need not require a cleave abouta closed path.

Embodiments described herein relate a method to cut transparentmaterials into one or more articles with specific predeterminedcontoured shapes, using cutting, isolation and removal processes thatexpose the high quality edge generated by the above-mentioned processeswithout damaging the article by the isolation and removal processes.FIG. 1 illustrates a parent glass substrate 10. Also shown is a first,inner, predetermined path 12 and a second, outer (relative to inner path12), predetermined path 14, wherein both first and second pathsrepresent closed paths. In the illustrated embodiment, first and secondpaths 12, 14 are circular paths, where second path 14 is concentric withfirst path 12, although in further embodiments the first and secondpaths need not be circular. In accordance with the embodiment of FIG. 1,first path 12 defines a first disc, hereinafter plug 16, comprising afirst radius r1, and second path 14 defining a second disc 18 comprisinga second radius r2. First path 12 and second path 14 define an annulus20 therebetween. That is, annulus 20, which is the article to beobtained, is second disc 18 removed from the surrounding material ofsubstrate 10 and with plug 16 removed from second disc 18. Accordingly,annulus 20 must be freed from the surrounding portion of substrate 10,and plug 16 must be removed from the surrounding material of second disc18. Release (removal) of annulus 20 from substrate 10 can beaccomplished using a cut around second path 14, and additional cuts(release lines) along paths 22 that ease the process for removing theannulus. However, for interior portions of substrate 10, such as plug16, no such cuts can be made as such cuts would damage the surroundingannulus, which in the present example is the commercial part ofinterest. Additionally, the processes described herein produce cuts withessentially zero kerf. Thus, while plug 16 may be isolated from thesurrounding material and thereby capable of moving independently, theplug remains captured within the annulus. The plug may be forced fromthe annulus, but with a high likelihood that damage to the annulus willoccur.

While the present disclosure describes in detail removal of both plug 16from second disc 18 to form a subsequent circular hole therein, andremoval of annulus 20 from the glass substrate, methods described hereinmay be used to remove a broad variety of articles of arbitrary shapes,including without limitation regular geometric shapes, such as circular,triangular, rectangular or slot shaped. Articles removed from thesubstrate may have radiused corners, or the corners may be sharp (e.g.,edges that intersect at an angle) features.

The challenge with forming an interior closed cut in a glass substrateand removing the resultant interior part to form an opening, for examplea central spindle hole in a memory disk substrate, is that, even ifsuitable closely-spaced defect lines are produced along a closed,predetermined path to form a fault line, and a crack propagates aroundthe path intersecting the defect lines, thereby isolating the interiorpart from the surrounding material, the cutting process is anessentially zero-kerf process. That is, the typical defect line producedby the process is about 1 micrometer in diameter, and thesurface-to-surface separation at the intervening crack between defectlines is essentially zero. Accordingly, even if the interior part can bemoved, it may catch against an edge of the surrounding material andcause chipping of the part, the surrounding material, or both if removalis attempted. Thus, when removing plug 16 from second disc 18 to formannulus 20, removal of the plug may damage the annulus. A challengingaspect of automating a separation and removal process is incorporatingsteps that allow the isolated interior part to drop from the surroundingmaterial without damage to the surrounding material. In respect of disc18, this is true for both the plug removed from the center of the seconddisc and the annulus portion itself. That is, damage to annulus 20 is tobe avoided both when removing plug 16 from disc 18 and when removingannulus 20 from the surrounding substrate material. The problem existsregardless of whether the material to be cut exhibits high internalstress and is easy to form cracks in, for example a chemicallystrengthened glass substrate like Gorilla® Glass, or if the material islow stress, for example a glass substrate suitable for forming a displaypanel, such as Eagle XG® glass, Corning Lotus™, Lotus™ XT, and/or Lotus™NXT glass. As used herein, high stress glass is a glass having a centraltension (in a thickness direction of the glass) equal to or greater thanabout 24 megaPascal (MPa). A low stress glass typically has a centraltension less than about 24 MPa. While Gorilla® Glass, Eagle XG® glass,Corning Lotus™, Lotus™ XT, and/or Lotus™ NXT glass have beenspecifically mentioned herein, the claims appended herewith should notbe so limited, as exemplary processes and methods are applicable toother glasses, such as alkaline earth boro-aluminosilicate glasses (withlow or no alkali), aluminosilicate glasses, alkali earth-containingglasses, and the like.

As described supra, the present disclosure is generally directed to amethod and apparatus for cutting and removing portions of a glasssubstrate. However, in particular embodiments, the present disclosure isdirected to a laser method and apparatus for precision cutting,isolation and removal of arbitrarily shaped articles from glasssubstrates in a controllable fashion, with negligible debris and minimaldamage to cut edges that preserves the strength of the article. Theresultant article may require only minimal or even no edge finishing(grinding and/or polishing), and in certain embodiments, may involveminimal or no finishing of major surfaces of the article. The methodrelies on the substrate material transparency and linear opticalabsorption at the wavelength of the laser used to form the defect linesat low laser beam intensity, which allows maintenance of a clean andpristine surface quality, and on the non-linear absorption induced byhigh laser beam intensity along the laser focus line. A key enabler ofthis process is the high aspect ratio of the defect created by theultra-short pulsed laser beam that allows creation of a defect lineextending between the major surfaces of the material to be cut. Inprinciple, this defect line can be created by a single laser pulse.However, if necessary, additional pulses can be used to increase thesize of the affected area (e.g., depth and width).

Using a short pulse picosecond laser and accompanying optics thatgenerate a focal line along the laser beam longitudinal axis (i.e., inthe direction of beam propagation), a series of defect lines can beformed at closely-spaced intervals along a predetermined path, orcontour, on a substrate, the defect lines extending through at least aportion of the thickness of the substrate, e.g., a glass sheet. Defectlines are typically less than a few micrometers in diameter. A series ofdefect lines along a path are referred to as a fault line, and theseries of defect lines can be joined by a series ofdefect-line-to-defect-line cracks, either self-formed due to existingstress in the substrate or due to stress induced by subsequent exposureto a heat source, for example a second laser beam, to thereby isolateone portion of the substrate from another portion of the substrate.

The optical method of forming a line focus can take multiple forms, forexample using donut shaped laser beams and spherical lenses, axiconlenses, diffractive elements, or other methods to form the linear regionof high intensity. The type of laser (picosecond, femtosecond, etc.) andwavelength (IR, green, UV, etc.) can also be varied, as long assufficient optical intensities are reached to create breakdown of thesubstrate material. The laser wavelength is typically chosen so that thesubstrate (e.g., glass sheet) is highly transparent to the radiation. Inthe case of glass, 1064 nanometer light is a commonly preferredwavelength, where high intensity pulsed lasers such as those usingNd:YVO₄ as the gain medium are available. When the laser pulse passesthrough these optics, the optical energy is formed into a linear regionof high intensity that can be extended through entire thickness of thesubstrate. More generally, the selected wavelength may be in a rangefrom about 2 micrometers to about 11 micrometers, for example, about10.6 micrometers, 5.32 micrometers, 3.55 micrometers or 2.66micrometers, although other wavelengths may be suitable depending on thematerial.

In some embodiments, the pulse duration of the individual pulses can bein a range from about 0.1 picoseconds to about 100 picoseconds, such asin a range from about 5 picoseconds to about 20 picoseconds, and therepetition rate of the individual pulses can be in a range from about 1kHz to about 4 MHz, such as in a range from about 10 kHz to about 650kHz. As the frequency increases, the speed with which the process canoperate increases. However, as the frequency increases, the energy perpulse decreases.

The laser creates defect lines that penetrate the glass substrate. Adefect line may include microcracking, but may also include internalopenings or voids, for example, of approximately 1 micrometer indiameter. These defect lines are generally spaced from about 1 to about20 micrometers apart, for example, in a range from about 0.5 to about 15micrometers, in a range from about 0.5 micrometers to about 3micrometers, or in a range from about 3 micrometers to about 10micrometers. For example, in some embodiments the periodicity betweenadjacent defect lines can be between 0.5 micrometers and 1.0micrometers. The defect lines can extend, for example, through theentire thickness of the glass substrate, and are typically perpendicularto the major (flat) surfaces of the substrate, although in furtherembodiments, the defect lines may extend through only a portion of thesubstrate thickness. Moreover, in some embodiments the defect lines maybe produced at an angle to the major surfaces of the substrate, forexample if chamfered edges are desired on annulus 20.

In addition to a single pulse operation at the aforementioned individualpulse repetition rates, the pulses can be produced in bursts of two ormore pulses (e.g., 3 pulses, 4 pulses, 5 pulses, 10 pulses, 15 pulses,20 pulses, or more) separated by a duration between the individualpulses within the pulse burst that is in a range from about 1 nanosecondto about 50 nanoseconds, for example in a range from about 10nanoseconds to about 50 nanoseconds, in a range from about 10nanoseconds to about 30 nanoseconds, for example about 20 nanoseconds,and the burst repetition frequency can be in a range from about 1kilohertz to about 4 Mhz. For a given laser, the time separation T_(p)between adjacent pulses (pulse-to-pulse separation) within a burst isrelatively uniform (e.g., ±10%). For example, for a laser that producesa pulse separation T_(p) of about 20 nanoseconds, the pulse-to-pulseseparation T_(p) within a burst can be maintained within about ±10%, orabout ±2 nanoseconds. The time between each “burst” of pulses (i.e.,time separation T_(b) between bursts) will be much longer (e.g.,0.25≤T_(b)≤1000 microseconds, for example in a range from about 1microsecond to about 10 microseconds, or in a range from about 3microseconds to about 8 microseconds). In exemplary embodiments, thetime separation T_(b) can be about 5 microseconds for a laser with apulse burst repetition rate, or frequency, of about 200 kHz. The laserburst repetition rate is related to the time T_(b) between the firstpulse in a burst to the first pulse in the subsequent burst (laser burstrepetition rate=1/T_(b)).

In some embodiments, the laser burst repetition frequency may be in arange from about 1 kHz to about 650 kHz. For example, the laser burstrepetition rates can be, for example, in a range from about 1 kHz toabout 300 kHz. The time T_(b) between the first pulse in each burst tothe first pulse in the subsequent burst may be in a range from about0.25 microseconds (4 MHz burst repetition rate) to about 1000microseconds (1 kHz burst repetition rate), for example in a range fromabout 0.5 microseconds (2 MHz burst repetition rate) to about 40microseconds (25 kHz burst repetition rate), or in a range from about 2microseconds (500 kHz burst repetition rate) to about 20 microseconds(50k Hz burst repetition rate). Individual pulses may have pulsedurations T_(d) of up to 100 picoseconds (for example, 0.1 picoseconds,5 picoseconds, 10 picoseconds, 15 picoseconds, 18 picoseconds, 20picoseconds, 22 picoseconds, 25 picoseconds, 30 picoseconds, 50picoseconds, 75 picoseconds, including all ranges and subrangestherebetween). The energy or intensity of each individual pulse withinthe burst may not be equal to that of other pulses within the burst, andthe intensity distribution of the multiple pulses within a burst may insome embodiments follow an exponential decay in time governed by thelaser design, although in other embodiments decay may not be evident.The exact timing, pulse duration, and burst repetition rate can varydepending on the laser design, but short pulses (T_(d)<20 picosecondsand preferably T_(d)≤15 picoseconds) of high intensity have been shownto work particularly well.

The average laser energy per burst measured at the substrate materialcan be greater than 40 microJoules per millimeter thickness of material,for example in a range from about 40 microJoules/mm to about 2500microJoules/mm, for example from about 200 microJoules/mm to about 800microJoules/mm. Put another way, the energy per burst is typically in arange from about 25 microJoules to about 750 microJoules, for example ina range from about 50 microJoules to about 500 microJoules, or in arange from about 50 microJoules to about 250 microJoules, including allranges and subranges therebetween. In some embodiments, the energy perburst can be in a range from about 100 microJoules to about 250microJoules. For example, for Corning 2320 non-ion exchanged glass witha thickness in a range from about 0.5 millimeters to about 0.7millimeters, 200 microJoule pulse bursts can be used to cut and separatethe glass, which gives an exemplary range of about 285 microJoules/mm toabout 400 microJoules/mm. Relative motion between the substrate and thelaser beam can then be used to create a fault line comprising a seriesof defect lines that trace out the shape of any desired part or parts(e.g., a plug).

For alkaline earth boro-aluminosilicate glasses (with low or no alkali)in particular, volumetric energy densities within of about 0.005microJoules/micrometer³ or higher can ensure a defect line is formed.However, such energy densities should be kept below about 0.100microJoules/micrometer³ so as to incur only minimal damage to the glass,for example in a range from about 0.005 microJoules/micrometer³ to about0.100 microJoules/micrometer³.

The energy of an individual pulse within the pulse burst will be lessthan the foregoing, and the exact individual laser pulse energy willdepend on the number of pulses within the pulse burst and the rate ofdecay (e.g., exponential decay rate), if any, of the laser pulses withtime. For example, for a constant energy per burst, if a pulse burstcontains 10 individual laser pulses, then each individual laser pulsewill contain less energy than if the same pulse burst had only 2individual laser pulses.

The use of a laser capable of generating such pulse bursts isadvantageous for cutting or modifying transparent materials, for exampleglass. In contrast with the use of single pulses spaced apart in time bythe repetition rate of the single-pulse laser, the use of a pulse burstsequence that spreads the laser energy over a rapid sequence of pulseswithin the burst allows access to larger timescales of high intensityinteraction with the substrate material than is possible withsingle-pulse lasers. While a single-pulse can be expanded in time, theintensity within the pulse must drop as roughly one over the pulsewidth. Hence, if a 10 picosecond single pulse is expanded to a 10nanosecond pulse, the intensity drops by roughly three orders ofmagnitude. Such a reduction can reduce the optical intensity to a pointwhere non-linear absorption is no longer significant, and thelight-material interaction is no longer strong enough to allow forcutting. In contrast, with a pulse burst laser, the intensity duringeach pulse within the burst can remain very high—for example three 10picosecond pulses spaced apart in time by approximately 10 nanosecondsstill allows the intensity within each pulse to be approximately threetimes higher than that of a single 10 picosecond pulse. Thus, the lasercan interact with the substrate over a timescale that is now threeorders of magnitude longer. This adjustment of multiple pulses within aburst allows for a manipulation of the time-scale of the laser-materialinteraction in ways that can facilitate greater or lesser lightinteraction with a pre-existing plasma plume, greater or lesserlight-material interaction with atoms and molecules that have beenpre-excited by an initial or previous laser pulse, and greater or lesserheating effects within the material that can promote the controlledgrowth of microcracks. The required amount of burst energy to modify thematerial will depend on the substrate material composition and thecharacteristics of the line focus used to interact with the substrate.The longer the interaction region, the more the energy is spread out,and higher burst energy will be required. A defect line is formed in thesubstrate when a single burst of pulses strikes essentially the samelocation on the substrate. That is, multiple laser pulses within asingle burst correspond to a single defect line in the substrate. Ofcourse, since the substrate is translated (for example by a constantlymoving stage), or the beam is moved relative to the substrate, theindividual pulses within the burst cannot be at exactly the samelocation on the substrate. However, the individual pulses are wellwithin 1 micrometer of one another, i.e., they strike the substrate atessentially the same location. For example, the individual pulses maystrike the substrate at a spacing, sp, from one another where 0<sp≤500nanometers. For example, when a substrate location is hit with a burstof 20 pulses, the individual pulses within the burst strike thesubstrate within 250 nm of each other. Thus, in some embodiments, thespacing sp may be in a range from about 1 nanometer to about 250nanometers, for example in a range from about 1 nanometer to about 100nanometers.

In some embodiments, an ultra-short (e.g., 10 picosecond) burst pulsedlaser can be used to create a high aspect ratio defect line in aconsistent, controllable and repeatable manner. The details of anexemplary optical setup that can be used to create suitable defect linesis described below and in U.S. Application No. 61/752,489, filed on Jan.15, 2013, the content of which is incorporated herein by reference inits entirety. The essence of this concept is to use an axicon lenselement in an optical lens assembly to create a region of high aspectratio taper-free defect lines using ultra-short (picoseconds orfemtosecond duration) Bessel beams. In other words, the axicon and otherassociated optical components condense the laser beam into a region ofgenerally cylindrical shape and high aspect ratio (long length and smalldiameter). Due to the high intensity created within the condensed laserbeam, nonlinear interaction of the laser electromagnetic field and thesubstrate material occurs and the laser energy is transferred to thesubstrate. However, in areas where the laser energy intensity is notsufficiently high (e.g., glass surface, glass volume surrounding thecentral convergence line), nothing happens to the substrate as the laserintensity in those locations is below both the linear and nonlinearthreshold.

As shown in FIG. 2, a laser (not shown) emits laser beam 30 at the beamincidence side of optical assembly 32. The optical assembly 32 convertslaser beam 30 into an extended laser beam focal line 34 on the outputside of optical assembly 32 over a defined distance along the laser beamaxis. Those skilled in the art will recognize that changes in the lengthof focal line 34 can occur due to changes in the refractive index, forexample between air propagation and propagation in the substrate. Thesubstrate 10 is positioned in the beam path, after the optical assembly32, overlapping at least partially the laser beam focal line 34. Opticalassembly 32 may include, for example, an axicon 36, a collimating lens37 and a focusing lens 38. Reference numeral 40 designates the majorsurface of the substrate facing optical assembly 32, while referencenumeral 42 designates the opposing major surface of substrate 10,usually parallel with major surface 40. The substrate thickness(measured perpendicular to the surfaces 40 and 42) is labeled d.

Optical assembly 32 forms what is termed a quasi-non-diffracting beam,which is a beam that diffracts or spreads much less rapidly thanconventional Gaussian laser beams. These optics are most often used tocreate what is termed a Gauss-Bessel beam, which is one form of anon-diffracting beam that can maintain a tight focus over a lengtheasily 100×, or even 1000×0 longer than a traditional Gaussian beam.

In the overlapping area of the laser beam focal line 34 with substrate10, the laser beam focal line 34 generates (assuming suitable laserintensity along the laser beam focal line 34) an induced absorption(non-linear absorption) in the substrate material that produces a defectline in the substrate material. Defect formation is not only local tothe region of the focal line, but occurs over the entire length of thefocal line within substrate 10. The average diameter of the laser beamfocal line 34 may be, for example, in a range from about 0.1 micrometersto about 5 micrometers, for example in a range from about 0.1micrometers to about 4 micrometers, for example in a range from about0.1 micrometers to about 3 micrometers, for example in a range fromabout 0.1 micrometers to about 2 micrometers, for example in a rangefrom about 0.1 micrometers to about 1 micrometer, while the focal regionextends for millimeters in length (e.g., in a range from about 0.5 toabout 10 millimeters).

As the foregoing shows, substrate material that is otherwise transparentat the wavelength λ of laser beam 30 is heated due to the inducednonlinear absorption along the focal line 34 to form a defect line. Theabove described process creates a piece with very characteristic edgescomprised of vertical striations. Each striation is the signature of asingle laser pulse, or a single burst of laser pulses and represents aportion of a defect line. As with the defect lines, these stria can beperiodically spaced approximately every 1 to 50 micrometers apart, forexample every 1 to 20 micrometers apart, for example in a range fromabout 5 to about 15 micrometers apart. The stria represents amodification of the substrate material by the focused laser energy,which results in a long linear damage track (the defect line) parallelto the laser beam axis. The substrate material in that region can bedensified or chemically altered. The defect line generally includescracks emerging therefrom that can extend approximately 5 to 10micrometers radially into the substrate, or in some cases up to 25micrometers, with the size of the crack generally being proportional tothe amount of laser energy deposited in the material. A defect line mayhave open regions, but is generally not a continuous hole through thethickness of the substrate. At the top and bottom of the defect linethere is frequently an open hole. The open region of the hole typicallyhas a diameter of less than 1 micrometer, but under some conditions canbe made large, such as up to 5 micrometers in diameter. The hole oftenhas a raised area or “crater rim” of ejected and melted material thatsurround it, typically exhibiting a diameter in a range from about 3micrometers to about 8 micrometers. FIG. 3 is a scanning electronmicroscope image of a typical defect line as seen on the surface of aglass substrate, showing the rim and ejecta. FIG. 4 is a scanningelectron microscope image of the glass substrate as seen in crosssection, showing a defect line along at least a portion of its length.

The use of defect lines to define the edges of a part provides highdimensional quality to the resultant article. Since the cracks thatisolate the article are guided by the defect lines, the spatialprecision and accuracy of the short pulse laser beam determines thedirection in which the crack propagates, and, in the example of anannular shape, results in an inner and outer radius made to a micrometerlevel of accuracy, for example less than 25 micrometer, such as lessthan about 15 micrometers, and typically about +/−5 micrometers, butcertainly tolerances. This is in contrast to mechanical processes, whichcannot guide a crack around such a radius. It is also in contrast toother laser processes, such a CO₂ laser cutting, where a crack isthermally propagated by guiding it with a hot spot formed from a CO₂laser beam, but is not guided by any pre-defined defects created in thesubstrate. The lack of guiding defects can lead to crack wander, whichmeans such tight (micrometer level) accuracy cannot be achieved. Otherlaser process, such as Gaussian focused UV or visible laser ablation toform a trench or crack at the top of the substrate also suffer from poordimensional control, as they tend to only control the crack at onesurface of the glass.

In spite of surface stria, the crack face resulting from separation ofthe substrate should be of high quality (regarding breaking strength,geometric precision, roughness and avoidance of re-machiningrequirements). Surface roughness in particular results from the spotsize or the spot diameter of focal line 34. To achieve a small spotsize, for example 0.5 micrometers to 2 micrometers in the case of agiven wavelength λ, of the laser, certain requirements are usuallyimposed on the input beam diameter and numerical aperture of opticalassembly 32.

To achieve the required numerical aperture, the optical assembly should,on the one hand, possess the required opening for a given focal lengthaccording to the known Abbe formulae (N.A.=n sin (theta), where nrepresents the refractive index of the glass, theta represents theaperture half angle, and theta=arctan (D/2f); where D represents theaperture diameter and f represents focal length). On the other hand, thelaser beam must illuminate the optical assembly up to the requirednumerical aperture, which is typically achieved by means of beamwidening, for example using beam widening telescopes between the laserand the focusing optics.

The spot size should not vary too greatly for the purpose of a uniforminteraction along the focal line. This can, for example, be ensured byilluminating the focusing optics only in a small, circular area so thatthe beam opening and thus the percentage of the numerical aperture varyonly slightly. Suitable optical assemblies 32 that meet these needs andcan be applied to generate focal line 34 include laser processing deviceCLT 45G available from Corning Laser Technologies.

It should be noted that focal line 34 can be produced and arranged suchthat focal line 34 lies entirely within substrate 10, crosses only onemajor surface, or crosses both major surfaces of the substrate. It ispossible to change the focus position of the optics sufficiently tocause only a portion of the depth of the substrate to be damaged. Insuch a case, the striation may extend from the top of the substrate tosomewhere in the middle of the substrate, or from the bottom of thesubstrate to somewhere in the interior of the substrate. In the instancewhere focal line 34 may be entirely within the bulk of the substrate, itshould be recognized that surface thresholds are different than bulkthresholds, so typically entrance and exit holes are still formed in thesubstrate by the incident beam, then areas with no damage, and then thedefect line. That is, although focal line 34 may lie entirely within thesubstrate, surface damage may still be present. In those cases it isstill possible to separate the part from the substrate, but full controlof the crack direction or separation contour may be compromised. Bestresults are achieved with focal line 34 extending to both major surfaces40, 42, as this improves the ability to isolate the part of interest andminimizes variations in edge strength. Thus, it is possible to achievevirtually ideal cuts while avoiding feathering and large particlegeneration at the surfaces of the substrate.

Depending on the material properties (optical absorption, coefficient ofthermal expansion (CTE), stress, composition, etc.) and laser parameterschosen for processing the selected substrate material, the creation of afault line alone can be enough to induce separation, and in some casesisolation of the article. Self-separation and/or self-isolation mayoccur as spontaneous events, without the addition of external mechanicalforce. This is the case for most strengthened glasses (those havingalready undergone ion-exchange before cutting) that have significant(i.e., equal to or greater than about 24 MPa) internal or centraltension (CT). In this case, secondary processes, such as mechanicallyapplied tension (e.g., bending) forces or heating (e.g., with a laserbeam) are generally not necessary to promote isolation (although notplug removal).

The foregoing notwithstanding, in some cases, pre-existing stresses, orstresses formed during creation of the fault line may not be sufficientto isolate the interior part automatically. The insufficiency of faultline formation itself to induce isolation is often the case fornon-strengthened glasses with insufficient residual stress, such asdisplay-type glass like Eagle XG®, Lotus™, Lotus™ XT, and/or Lotus™ NXTor otherwise ion-exchangeable glasses that are cut before anyion-exchange step. Thus, a secondary process step may be necessary topromote isolation. For example, isolation can be achieved, after thecreation of a fault line, by application of mechanical force or byre-tracing the previous path followed during creation of the fault linewith an infrared laser beam (e.g., CO₂ or CO laser beam) to locally heatthe substrate along the path and create sufficient thermal stress,without ablation, to force the parts to isolate. That is, to create oneor more full-body cracks along the fault line that then isolate theinternal part. Another option is to have the laser only startseparation, for example by only partially traversing the predeterminedpath, wherein isolation is performed manually, for example by bending orby other applications of force. The optional laser separation can beperformed with a defocused continuous wave CO₂ laser emitting at awavelength in a range from about 9 micrometers to about 11 micrometers,for example 10.6 micrometers, and with power adjusted by controlling thelaser duty cycle, although in further embodiments, other wavelengths andlaser mediums may be used (for example a CO laser). Focus change (i.e.,extent of defocusing) can be used to vary the induced thermal stress byvarying the spot size of the laser beam on the surface of the substrate,where the spot size is defined as 1/e² of the peak intensity. Aftergeneration of the fault line, laser induced separation and isolation cangenerally be achieved using a power at the substrate surface in a rangefrom about 40 watts to 400 watts, a spot size in a range from about 2millimeters to about 12 millimeters, and a traverse rate of the laserbeam along the fault line of in a range from about 50 millimeters/secondto about 3000 millimeters/second, for example in a range from about 80millimeters/second to about 500 millimeters/second. If the spot size istoo small (i.e., less than about 1 millimeter), or the laser power istoo high (greater than about 400 watts), or the scanning speed is tooslow (less than about 1 millimeter/second), the substrate may be overheated, creating ablation, melting or thermally generated cracks, whichare undesirable because they can reduce the edge strength of theseparated parts. Preferably the laser beam scanning speed is greaterthan about 50 millimeter/second to induce efficient and reliable partseparation. However, if the spot size created by the laser is too large(greater than about 20 millimeters), or the laser power is too low (lessthan about 10 watts, or in some cases less than about 30 watts), or thescanning speed is too high (greater than about 500 millimeters/second),insufficient heating can occur, which may result in a thermal stress toolow to induce reliable part separation.

In some embodiments, a CO₂ laser operating at a power of 200 watts maybe used, with a spot diameter at the glass surface of approximately 6millimeters, and a scanning speed of about 250 millimeters/sec to inducepart separation for 0.7 millimeter thick Corning Eagle XG® glass thathas been modified with the above-described picosecond laser. A thickersubstrate may require more laser thermal energy per unit time toseparate than a thinner substrate, or a substrate with a lower CTE mayrequire more CO₂ laser thermal energy to separate than a substrate witha lower CTE. Separation along the fault line can occur very quickly(e.g., within about 1 second) before or after the laser spot passes agiven location, for example within 100 milliseconds, within 50milliseconds, or even within 25 milliseconds.

However, even if the substate has sufficient internal stress to startself-separation or self-isolation after the formation of the fault line,the geometry of the part may prevent the part from being easily removedfrom the surrounding substrate material. This is especially true whenthe part to be removed is an interior portion of another part, forexample plug 16. Accordingly, the plug may remain in place due to lackof sufficient clearance (gap) between the plug and the surroundingsubstrate material. Cracks may propagate between the defect lines thatisolate the plug, but no room exists between the plug and thesurrounding substrate material to allow the plug to be removed from theparent substrate material without damage to the surrounding material.Release lines will only destroy the surrounding part of interest.

Referring now to FIGS. 5 and 6, a method will now be described forcutting and removing an article from a glass substrate 10, although itshould be understood that the method can be applied to other substratematerials. The method may include a step of positioning a parent glasssubstrate 10 on a planar supporting substrate 100. The glass substratethickness d may be in a range from about 50 micrometers to about 3millimeters, for example in a range from about 100 micrometers to about2 millimeters, for example in a range from about 300 micrometers toabout 1 millimeters. For example, in some embodiments, the glasssubstrate may have a thickness in a range from about 0.5 millimeters toabout 0.7 millimeters. Preferably, glass substrate 10 is a fusion-formedglass substrate, wherein first and second major surfaces 40, 42 have notbeen ground or polished prior to forming defect lines in the glasssubstrate, although in further embodiments the glass substrate mayinclude first and second major surfaces that have been ground and/orpolished, and in further embodiments, the glass substrate 10 may beformed by other forming processes, including without limitation, floatand slot forming processes. The two surfaces of a glass substrate formedby the fusion process are typically not in contact with mechanicalhandling surfaces while the glass is at high temperature. This leads tothe ability to form large sheets of glass with pristine surfaces,without the need for polishing to remove surface contamination or otherdefects. The surfaces of fusion formed glass substrates have nopolishing marks, and no concentrations of Sn near the glass edges. Thesurface roughness of fusion formed sheets is typically less than 1nanometer Ra, but frequently is less than about 0.5 nanometer Ra.

In contrast, glass made using a conventional float process has one sidethat is exposed to molten tin (Sn) during the forming process. While thefloat glass process often can create glass at lower cost than the fusiondraw process, it has a number of drawbacks. The presence of tin createsa contaminant or chemical signature within the glass sheet. Furthermore,the float process does not make glass that is as smooth as the fusiondraw process. This means the Sn side must be polished to meet finalroughness criteria, and also to remove the Sn contaminant itself. For atleast the above reasons, it is preferred to employ fusion formed glasssheets.

In embodiments, glass substrate 10 may comprise a coefficient of thermalexpansion in a range from about 30×10⁻⁷/° C. to about 40×10⁻⁷/° C. overa temperature range from about 0° C. to about 300° C., for example in arange from about 30×10⁻⁷/° C. to about 40×10⁻⁷/° C., for example in arange from about 30×10⁻⁷/° C. to about 36×10⁻⁷/° C., including allranges and subranges therebetween. An anneal point of the glasssubstrate can be equal to or greater than about 700° C., for exampleequal to or greater than about 800° C. In some embodiments, an annealpoint of the glass substrate is in a range from about 700° C. to about820° C., for example in a range from about 710° C. to about 730° C.,while in other embodiments an anneal point of the glass substrate can bein a range from about 800° C. to about 810° C. Anneal point can bemeasured, for example, using ASTM C336 (fiber elongation) or ASTM C598(beam bending). In embodiments, the glass substrate comprises acompaction equal to or less than about 35 ppm after being subjected to atemperature of 600° C. for 30 minutes and allowed to cool to roomtemperature (23° C.), for example less than about 20 ppm. Compaction maybe measured by placing multiple fiducial markings on the substrate, andsubjecting the substrate to a thermal cycle, and then measuring therelative positional change or shrinkage between the fiducial markings.

In embodiments, an average surface roughness (Ra) of the glass substrate(major surfaces), prior to any grinding or polishing, is equal to orless than about 0.5 nm. The glass substrate may comprise tin on an oxidebasis (SnO₂) in an amount equal to or less than about 0.5 wt. %, forexample equal to or less than about 0.3 wt. %, for example equal to orless than about 0.2 wt. %. In some embodiments the glass substrate maycomprise less than about 0.15 wt. % SnO₂, although in furtherembodiments the glass substrate may comprise essentially no SnO₂. Theglass substrate may in some embodiments include a density equal to orgreater than about 25 grams/cm³, and a Young's modulus in a range fromabout 75 GPa to about 90 GPa, for example in a range from about 80 GPato about 85 GPa, for example in a range from about 82 GPa to about 84GPa, including all ranges and subranges therebetween. Glass density canbe measured using a calculating digital density meter. Young's moduluscan be measured using ASTM E111, e.g., E111-04(2010). The glasssubstrate may comprise a softening temperature in a range from about900° C. to about 1100° C., for example in a range from about 950° C. toabout 1050° C., for example in a range from about 970° C. to about 1050°C., for example in a range from about 1025° C. to about 1050° C., forexample in a range from about 1040° C. to about 1050° C. In someembodiments, the glass substrate may include a softening temperature ina range from about 1040° C. to about 1050° C., including all ranges andsubranges therebetween. The softening temperature can be measured, forexample, using ASTM C338.

The glass is preferably free of alkali metal oxides, since alkali metalscan migrate over time and with high temperature exposure, causingchemical contamination and poisoning of other layers in the system suchas the magnetic layers of the hard disk. For example, in someembodiments the glass is an alkali metal oxide free aluminoborosilicateglass. As used herein, alkali metal oxide free means equal to or lessthan about 0.1 wt. % alkali metal oxide. The glass preferably containssubstantially no As₂O₃, wherein the phrase “contains substantially noAs₂O₃” means that no As₂O₃ is contained other than that originating, asimpurities, from raw materials, or the like, and the content of As₂O₃ ina glass composition is 0.1% by weight or lower (preferably, 50 ppm orlower). The glass preferably contains substantially no Sb₂O₃, whereinthe phrase “contains substantially no Sb₂O₃” means that no Sb₂O₃iscontained other than that originating, as impurities, from rawmaterials, or the like, and the content of Sb₂O₃ in a glass compositionis 0.1% by weight or lower (preferably, 50 ppm or lower).

Support substrate 100 comprises a first major surface 106 and a secondmajor surface 108, wherein second major surface 104 of glass substrate10 is positioned on first major surface 106 of support substrate 100.Support substrate 100 is shown separated from glass substrate 10 inFIGS. 5, 10, 11 and 12 for clarity only—in practice the glass substratemay be positioned directly on top of the support substrate. Supportsubstrate 100 can include one or more recesses 110 in surface 106 suchthat when parent glass substrate 10 is positioned on support substrate100, the location of inner predetermined contours located on the parentglass substrate 10 are positioned over respective recesses. That is, arecess 110 can be positioned beneath each location on parent glasssubstrate 10 at which an inner fault line will be formed. Each recess110 can serve several purposes. First, the recesses 110 can provide agap between the portions of the glass substrate 10 that are heatedduring subsequent processing. In some embodiments, support substrate 100may comprise a suitable polymer material to prevent marring and damageto the glass substrate. The polymer material may include a low meltingtemperature and thus be easily damaged by heat. Alternatively, thepolymer material may include a high melting temperature such that thepolymer is unaffected by heating.

Second, recesses 110 provide a region that can capture a plug 16 definedby the inner fault line as the plug is released from the glasssubstrate. In addition, each recess 110 may optionally include a passage112 extending from a floor or bottom of the recess to the oppositesurface of the support substrate, e.g., surface 108. Passage 112 may bein fluid communication with a vacuum source (not shown), so that avacuum can be applied to the recesses to aid in removal of plug 16 fromthe glass substrate 10. Moreover, support substrate 100 may includeadditional passages 114 positioned outside recess 110. The additionalpassages 114 may also be placed in fluid communication with a vacuumsource (not shown), which vacuum, when applied to the additionalpassages 114, aids in securing or otherwise fixing a position of glasssubstrate 10 to support substrate 100. The vacuum can be discontinuedwhen glass substrate 10 is to be removed from support substrate 100.However, in other embodiments, glass substrate 10 may be secured tosupport substrate 100 by other fixing means, for example, and withoutlimitation, by clamping or taping, or any other suitable fixing methodknown in the art. For example, in some embodiments, support substrate100 may be held in position electrostatically.

The method may further comprise creating fault lines for the intendedglass article (e.g., annulus 20) using a method or methods describedherein above, wherein a pulsed laser beam is used to create a successionof defect lines along a predetermined path by producing a focus linethat extends through the thickness d of the glass substrate. Forexample, referring to FIG. 5, laser 116 generating pulsed laser beam 118may be used to create a succession of defect lines 120 alongpredetermined paths to form a plurality of fault lines, represented bydotted lines in FIG. 6. Defect lines 120 may be spaced apart from eachother by a distance p in a range from about 1 micrometer to about 20micrometers as described previously (see FIG. 7). The fault lines arecoincident with the predetermined paths.

In the embodiment shown in FIGS. 5 and 6, the fault lines include afirst, inner circular fault line 122 coincident with a first, inner path12 (see FIG. 1) comprising a first radius and an second, outer circularfault line 124 coincident with a second, outer path 14 (see FIG. 1) andconcentric with inner fault line 122 and further including a secondradius greater than the first radius, the inner and outer fault linesapproximating an annulus 20 therebetween. In embodiments, the firstradius can be in a range from about 33 millimeters to about 34millimeters and the second radius can be in a range from about 9millimeters to about 11 millimeters. In other embodiments, the firstradius can be in a range from about 47 millimeters and 48 millimetersand the second radius can be in a range from about 12 millimeters toabout 13 millimeters, although in further embodiments, the first andsecond radii can be greater than or less than the distances cited above.

The plurality of fault lines may further include release lines 126.Release lines 126 facilitate removal of annulus 20 from the parent glasssubstrate 10. For example, some release lines may extend from edges 128a-128 d of glass substrate 10 to outer fault lines 122. In someembodiments, inner and outer fault lines 122, 124 are created first,prior to creation of release lines 126. In the embodiment shown in FIG.6, release lines 126 approach outer fault lines 124 at approximately 90degrees, although in further embodiments, release lines 126 may approachouter fault lines 124 at other angles. For example, in some embodiments,release lines 126 may approach outer fault lines 124 at a shallow anglesuch that an individual release line is approximately tangent to anouter fault line. In the instance where a release line approaches anouter fault line approximately orthogonally, the outer fault line 124should be formed prior to forming the approaching release line.

To illustrate why the order for creating fault lines can be important,consider the following example. There are interactions when the laserattempts to create a defect line in close proximity of another defectline. Energy in the line focus of the laser beam should be focused allthe way through the thickness of the glass substrate. However, if thereis an existing defect line nearby (typically within a few hundredmicrometers), this defect line will intercept some of the cone of raysthat form the line focus, and the defect line will scatter or obscurepart of the laser energy that would otherwise focus deep in the glassand form a new defect line (the degree of interaction depends on thesolid angle of the cone of rays intercepted). This may result in anincomplete defect line through the thickness of the glass substrate, andin some instances may prevent the formation of a defect line. When theglass parts are separated, an incomplete defect line, or the lack of adefect line, can result in the crack wandering. Typically this wanderingis referred to as “shadowing”, and can happen not only in the vicinityof pre-existing defect lines, but also in the vicinity of edges of theglass substrate. The exact proximity where shadowing effects areimportant depends on many things, such as the numerical aperture of theoptics, the thickness of the glass substrate, the laser energy used, theglass composition, etc. Therefore, it is preferable to complete faultlines for the desired article first (e.g., inner and outer fault lines122, 124), so that shadowing effects do not affect the ability to createwell-defined fault lines for the desired article.

Once fault lines 122, 124 and release lines 126 are formed, it may benecessary to create an intersecting crack that joins each defect linealong a fault line to an adjacent defect line to obtain isolation of aninterior part. This is typically the case for low residual stress glasssubstrates, for example non-strengthened glass substrates such asnon-ion-exchanged or non-thermally tempered glass substrates whereinsufficient residual stress exists for self-initiated crack formation.Accordingly, a heat source, for example an infrared heat source, such asan infrared laser (e.g., a CO₂ or CO laser), may be used to propagate acrack between adjacent defect lines. In respect of the foregoing innerand outer fault lines 122, 124, the heat source may be traversed overthe fault lines to induce sufficient thermal stress into the glasssubstrate to drive a crack between the defect lines. For example, alaser beam from a CO₂ laser may be traversed along the same path used toform a particular fault line such that the laser beam is incident alongthe fault line, although in further embodiments, other laser types maybe used. Laser heating along the fault line may be performed bydeveloping relative motion between the glass substrate and the laserbeam, either by keeping the glass substrate stationary and traversingthe laser beam, by keeping the laser beam stationary and moving theglass substrate, or by moving both the glass substrate and the laserbeam. For example, the laser may be positioned on a gantry capable ofmovement in at least two dimensions (e.g., a plane parallel with a planeof glass substrate 10), although in further embodiments, the gantry mayalso be capable of movement of the laser in a third dimension, i.e.,perpendicular to the glass substrate major surfaces. In someembodiments, multiple lasers may be used to heat fault lines when thereare many fault lines to be heated, thereby reducing process time. Insome embodiments, a single laser may be employed, with a laser beam fromthe single laser directed to a beam splitting head that divides thelaser beam into a plurality of individually controllable laser beams.Splitting the laser beam may reduce process time, but may also decreasethe power to each individual laser beam, requiring greater output fromthe single laser source. In still other embodiments, glass substrate 10may be placed within a heated oven to thermally shock the glasssubstrate and form intersecting cracks. This may also reduce processtime, but may introduce greater difficulty in handing, particularly forlarge glass substrates.

It should be noted however, that just as in the formation of the faultlines and release lines, the order for driving the crack through thefault lines and release lines (i.e., separation) should be considered.

To illustrate why the order in which cracks are driven can be important,consider this second example. If cracks are first driven within therelease lines, when the crack reaches the edge of the release line rightnext to an adjacent fault line, there is nothing to stop the crack. Thusthe crack can continue to propagate into the part resulting in adefective part.

FIG. 8 shows a glass substrate 10 comprising an annulus 20 definedbetween first, inner fault line 122 and second, outer fault line 124,depicted as dotted lines. Neither first fault line 122 nor second faultline 124 has been consolidated by a crack that extends along the faultlines between adjacent defect lines. FIG. 7 further depicts four releaselines 126 a-126 d, wherein a crack has been driven along fault line 126a using a suitable heat source, for example an infrared laser beam.Accordingly, release line 126 a is shown as a solid line. As the crackpropagates along release line 126 a, as indicated by arrow 128, itencounters second fault line 124. Since no crack yet exists at secondfault line 124, the crack propagating along release line 126 a is freeto extend beyond second fault line 124, and in the process forms a crackinto the desired part (i.e., annulus 20), as indicated by crack portion130. This can be mitigated, for example by ending the release linesfurther away from the desired part edge. However, the appropriatedistance depends on such factors as glass composition, thickness, laserpower, speed, humidity, etc. Thus, it is preferable the consolidatingcracks be created along the fault lines defining the desired part priorto driving cracks along the release lines. In this instance, this meansdriving a crack around second fault line 124 prior to driving a crackalong release line 126 a.

While the foregoing discussion dealt largely with orthogonal (or nearlyorthogonal) intersection between release lines and fault lines, asnoted, release lines can also approach fault lines tangentially. See,for example, FIGS. 9A-9D illustrating a portion of a fault line 124, inthis instance a portion of a circular fault line, and a tangentialrelease line 126 that overlaps with the fault line. It should first benoted that as the crack propagating along release line 126 (indicated bysolid line 132) approaches the fault line, shadowing can occur.Moreover, if, as shown in FIG. 9A crack propagation (separation) beginsat a release line prior to separation along the fault line, thepropagating crack may jump from the release line to the fault line asindicated by arrow 134 and continue around fault line 124 (as indicatedby solid line 136). On the other hand, if separation is performed on thefault line prior to the release line, as shown in FIG. 7B, the oppositecan occur, where the propagating crack jumps from the fault line to therelease line, as indicated by arrow 140. While the attached “dog ear” ofglass 142 is typically small and can be removed, for example bygrinding, more grinding that would otherwise be needed may need to beperformed, and additional inspection may be required. Similarly, thecrack may jump from the fault line to the release line, as shown in FIG.7C, resulting in incomplete separation of the part. The problemsassociated with tangential release lines can be mitigated if, forexample, release lines terminate prior to reaching the fault line suchthat there is a gap G between the terminal end of the release line 126and the fault line 124, as shown in FIG. 7D. In the embodiment of FIG.7D, separation can be performed along fault line 124 without danger ofthe propagating crack jumping to either of the release lines 126. Oncethe separation along fault line 124 is competed, separation along therelease lines 126 can be performed.

It should be further noted that different laser conditions can be usedwhen forming defect lines for the release lines than for the faultlines. For example, more “aggressive” laser conditions (e.g., greaterpulse energy) can be used for the release lines, since edge quality ofless of a concern that for the fault lines that define the edges of thedesired part.

FIG. 10 is a cross sectional view of glass substrate 10 positioned onsupport substrate 100, showing plugs 16. In the view shown in FIG. 10,defect lines have been produced, such as in accordance with but notlimited to methods described herein. As shown, the plugs 16 arepositioned over recesses 110.

In the instance where stress produced by the formation of the defectlines is insufficient to isolate the plugs 16 from the surroundingsubstrate via self-initiated separation, an optional step may beperformed, illustrated in FIG. 10, wherein a heat source, e.g., aninfrared laser 144 (e.g., a CO₂ or CO laser) generating a laser beam 146is used to traverse the laser beam over the fault lines and releaselines produced during the creation of the defect lines, to promoteseparation. That is, by driving a crack along the fault lines andrelease lines.

In some embodiments, a plurality of lasers may be used to reduceproduction time. This optional step may be necessary, for example, ifsubstrate 10 lacks the requisite central tension to promoteself-isolation. It should be emphasized that the heating of the faultline is performed under conditions selected such that no ablation,melting or vaporization of the glass substrate occurs. To that end,laser beam 146 may be defocused to prevent overheating of the glasssubstrate as described in detail above.

Once separation and/or isolation has been achieved, either byself-isolation (for high central tension substrates), or inducedisolation via heating of the fault and release lines, in a subsequentstep, plugs 16 may be heated. For example, in some embodiments a laser150, for example a CO₂ laser, producing laser beam 152 (as shown in FIG.11) may be employed. Optionally, the laser may be the same laser used inthe previous optional separation step, i.e., laser 146. In accordancewith the present embodiment, plugs 16 are heated such that only aportion of each plug is heated, for example to a temperature equal to orgreater than the softening temperature of the plug material (e.g.,glass). A number of heating techniques may be used. For example, in oneembodiment, laser beam 152 is directed at the center of the plug,heating only the central portion of the plug, for example to atemperature equal to or greater than a softening temperature of theplug. In another embodiment, laser beam 152 may be traversed over theplug along a path of substantially the same shape as predetermined path12 defining the plug but spaced apart from that path. For example, ifpredetermined path 12 is a circular path, laser beam 152 may betraversed over the plug along a circular path spaced apart and interiorto path 12. The laser beam may be traversed along the path only a singletime, or in other embodiments the laser beam may be traversed over thepath multiple times. In some embodiments, laser beam 114 may betraversed over multiple paths, for example multiple circular paths ofdifferent diameter, the multiple paths spaced apart from each other. Instill other embodiments, laser beam 152 may be traversed over plugs 16along a spiral path spaced apart from and interior to first path 12. Itshould be noted that, unlike the instance when a CO₂ laser is used toheat the fault line, either by traversing directly over the fault line,or close to it, in the present instance, heating of the plug isperformed relatively far from the predetermined contour defining theplug. Additionally, whereas before the laser beam may be a defocusedlaser beam to avoid overheating of the plug, in this situationoverheating is desired.

Traverse of the laser beam may be accomplished, for example, with agalvometer, although in further embodiments, an axicon can be used tocreate a ring-shaped laser beam, thereby avoiding in some embodimentsthe need to traverse the laser beam. In some embodiments, the laser beammay be mounted on a gantry capable of at least two dimensional movementin a plane parallel with the glass substrate. In further embodiments,the gantry may be capable of three dimensional movement and includemovement perpendicular to the plane of the glass substrate. In otherembodiments, relative motion can be provided by moving the substrate andmaintaining the laser assembly stationary.

While not wishing to be bound to theory, it is thought the heating ofplug 16 produces deformation of the plug, for example by slumping of theplug under its own weight. Accordingly, once heating of plugs 16 iscompleted, the plugs are allowed to cool for a time sufficient that theplugs fall from the glass substrate. Suitable cooling times aretypically in a range from about 10 seconds to 40 seconds, for example ina range from about 20 seconds to about 40 seconds, for example in arange from about 25 seconds to about 35 seconds. It is believed theheating of the plugs causing slight slumping of the plugs and coolingshrinks the plugs 18, thereby producing a sufficient gap between theplugs and the surrounding glass substrate to facilitate removal of theplugs. In such an instance, a diameter of the plug at a “top” surface ofthe plug (the surface of the plug that is heated, for example, thesurface upon which the heating laser beam impinges) after heating andsubsequent cooling is less than the diameter of the top surface beforeheating. Additionally, a diameter of the bottom surface (opposite theheated surface) after the heating and subsequent cooling is similarlyless than the diameter of the bottom surface before heating. Thedifference between the two diameters (top and bottom) is one ofmagnitude. In the present embodiment, the diameters of the top surfaceand the bottom surface are equal, or substantially equal (withinmeasurement precision). However, after heating and subsequent cooling ofthe plug central region, the diameter of the upper surface of the plugis less than the diameter of the lower surface of the plug. Forced(active) cooling of the plugs can be used subsequent to the heating, butis generally unnecessary and could in some instances produce non-uniformcooling, as both heating and cooling should be uniform to preventasymmetric stresses and non-uniform shape, i.e., it is desirable toproduce a consistent gap around the plug to prevent contact between theplug and the surrounding substrate, which can result in chipping.Indeed, it has been found that in most cases, upon cooling passively,the plugs typically fall from the substrate via their own weight,without the need for additional force to be applied.

In an optional step shown in FIG. 12, if desired, a vacuum can beapplied to passages 104, as indicated by arrows 160, which reduces thepressure within recesses 110. As a result, air pressure above the plugs16, indicated by arrows 162, can be used to assist extraction of plugs16 from glass substrate 10 and into recesses 102. Alternatively, amechanical force may be applied against the plugs 16, for example by apush rod or pipe.

After removal of plugs 16 from glass substrate 10, other parts ofsubstrate 10 can be removed, including peripheral (scrap) pieces joinedby release lines 126 so that annulus 20 can be removed.

The processes described herein can be used to quickly produce multiplearticles, for example multiple annuli, from a single substrate. Articlescan be closely positioned on the substrate to maximize materialutilization. For example, FIG. 13 illustrates how hexagonal closepacking can be used to maximize the utilization of glass substrate 10.In some embodiments, substrates can be stacked, wherein multiplesubstrates positioned one on top of the other, can have defect linesproduced simultaneously in the stacked substrates, provided the focalline is made sufficiently long. However, forming defect lines inmultiple substrates simultaneously still may require heating along thepaths followed by the defect line laser to promote crack propagation asin un-stressed single substrates. Thus, multiple substrates may includethe additional step of separating the stacked substrates into singlesubstrates to perform the subsequent heating step.

In other embodiments, other methods of removing plug 16 may be used.More generally, the gap between the outer diameter of the plug 16 andthe inner diameter of the annulus 20 should be increased in accordancewith the following equation:

D _(initial)>sqrt(D _(final) ² +P _(thickness) ²),  1)

Where D_(initial) represents the initial diameter of plug 16, D_(final)represents the final diameter of the plug, and P_(thickness) is thethickness of the plug (which should be equivalent to the thickness Th ofthe glass substrate). Said differently, when the maximum length of adiagonal line extending from an upper edge of the plug to a bottom edgeof the plug, the diagonal in the same plane as a diameter of the plug(the plane being perpendicular to the major surfaces of the plug and thediameter of the plug lying in the same plane) is less than the initialdiameter of the plug, the plug should drop from the glass substrate. Asan example, for a plug with an initial diameter D_(initial) of 25millimeters and a thickness P_(thickness) of 0.7 millimeters, therequired shrinkage of the plug is greater than 392 ppm. In addition todistorting the plug as previously described, other methods of reducingthe final diameter of the plug, or the inside diameter of thesurrounding glass (e.g., annulus 20). Such methods can include activecooling of the plug. In this instance, rather than heating a centralportion of the plug, then cooling, or allowing the plug to passivelycool, the plug can be actively and rapidly cooled, for example bydirecting a spray or stream of liquid nitrogen, or similar fluid, at theplug, thereby causing the plug to contract and forming a sufficientlylarge gap between the plug and the surrounding material that allows theplug to be removed without damage to the surround material. In otherembodiments, the entire glass substrate, include isolated parts, can beheated, for example in an oven, after which the plug can be cooled. Forexample, the glass substrate can be heated to a suitably hightemperature, e.g., about 112° C. based on a CTE of about 3.5 ppm), afterwhich the plug can be cooled to a temperature of about 0° C., again bythe use of liquid nitrogen or other sufficiently cold fluid.

The methods described herein provide the following benefits that maytranslate to enhanced laser processing capabilities and cost savings andthus lower manufacturing cost. The cutting process described hereinoffers full separation (isolation) of interior contours being cut. Themethods described herein are capable of completely removing plugs from aparent substrate in a clean and controlled fashion in ion-exchangeableglass (such as Gorilla® glass, Corning glass codes 2318, 2319, 2320 orthe like) as produced by the fusion draw process, or other glass formingprocesses, before or after the glass part has undergone chemicalstrengthening. The methods described herein also offer reducedsub-surface defects and excellent edge quality. Due to the ultra-shortpulse interaction between laser and material, there is little thermalinteraction and thus a minimal heat affected zone that can result inundesirable stress and micro-cracking outside the fault lines. Inaddition, the optics that condense the laser beam into the glass createsdefect lines that are typically in a range from about 2 micrometers toabout 5 micrometers in diameter on the surface of the part. The defectlines may be periodically spaced apart, wherein the spacing can be in arange from about 1 micrometer to about 50 micrometers, for example in arange from about 1 micrometer to about 20 micrometers, such as in arange from about 5 micrometers to about 15 micrometers. After removal ofthe parts, the subsurface damage is typically less than about 75micrometers, and can be adjusted, if desired, to be less than about 25micrometers. The roughness of the separated surface (or cut edge), canbe controlled via the spot size or the spot diameter of the focal line.A roughness of the separated (cut) edge surface, which can be, forexample, in a range from about 0.1 to about 1 micrometers, or forexample in a range from about 0.25 to about 1 micrometers, can becharacterized, for example, by an Ra surface roughness statistic(arithmetic average of absolute values of the heights of the sampledsurface, which include the heights of bumps resulting from the spotdiameter of the focal line). The surface roughness generated by thisprocess is often less than about 0.5 micrometers (Ra), and can be as lowas 0.1 micrometers (Ra), although edge surface roughness and edgestrength were unexpectedly found to be only weakly correlated. Inaddition, if mechanical finishing processes such as grinding andpolishing are later used to modify the edge shape, the amount ofmaterial removal required will be lower for parts with less sub-surfacedamage. This reduces or eliminates finishing steps and lowers part cost.The plug release process described herein takes full advantage of thehigh-quality edge created by this line-focus picosecond laser cuttingprocess such that removal of the interior glass material is done in amanner that cleanly releases the glass along the fault line, andproduces little to no ablative damage, micro-cracking, or other defectsto the desired part edge.

Unlike processes that use a focused laser to purely ablate materialalong given path, the laser processes disclosed herein can produce afault line in a single pass. The fault line may be created by picosecondlaser processes described herein at speeds in a range from about 50millimeters/second to about 3000 millimeters/second, depending on theacceleration capabilities of the stages involved. This is in contrast toablative drilling methods, where material is removed “layer by layer”and requires many passes or long residence times per location of thelaser beam.

The methods described herein are capable of cutting and separating glassor other transparent brittle materials in a clean and controlledfashion. It is very challenging to use conventional ablative or thermallaser processes because they tend to trigger heat affected zones thatinduce micro-cracks and fragmentation of the glass into several smallerpieces. The characteristics of the laser pulses and the inducedinteractions with the material of the disclosed methods avoid theseissues because defect creation occurs in a very short time scale and thematerial transparency to the laser beam used to form the defect linesminimizes the induced thermal effects. Since the defect line is createdwithin the substrate, the presence of debris and adhered particlesduring the cutting step is virtually eliminated. If there are anyparticles resulting from the created defect line, they are wellcontained until the part is separated.

The methods described herein enable the cutting and separation of glassand other substrates following many forms and shapes, which can be alimitation in other competing technologies. Small radii may be cut(e.g., less than about 2 millimeters), allowing creation of small holesand slots (such as required for speakers and/or microphones in cellphone applications).

In some embodiments, a plurality of substrates may be stacked, forexample two substrates, three substrates or more substrates, wherein thelaser beam focal line extends through each substrate of the stack ofsubstrates, thereby forming a plurality of defect lines that extendthrough each substrate of the stack of substrates.

Processes to fabricate glass plates from incoming glass panels to thefinal size and shape can involve several steps that encompass cuttingthe panel, cutting to size, finishing and edge shaping, thinning theparts down to their target thickness, polishing, and even chemicallystrengthening in some cases. Elimination of any of these steps willimprove manufacturing cost in terms of process time and capital expense.The methods described herein may reduce the number of steps, forexample, by reducing debris and edge defects generation, and thepotential elimination of washing and drying stations, and cutting thesample directly to its final size, shape and thickness, therebyeliminating the need for finishing lines.

Thus, according to some embodiments, a glass article has at least oneinner contour with a plurality of defect lines (or portions thereof)extending perpendicular to the face of the glass sheet at least 250micrometers, the defect lines each having a diameter less than or equalto about 5 micrometers. In some embodiments, the glass article comprisesdefect lines that extend the full thickness of the substrate. Thedistance between the defect lines can be, for example, less than orequal to about 7 micrometers. In some embodiments, the smallestdimension or width of the interior contour defined by the inner contouredge can be less than about 5 millimeters, for example it may be 0.1millimeters to 3 millimeters in width (or diameter), e.g., in a rangefrom about 0.5 millimeters to about 2 millimeters, although in furtherembodiments, the inner contour edge can have larger dimensions, such asin a diameter range from about 10 millimeters to about 100 millimeters,for example in a range from about 20 millimeters to about 50millimeters. According to some embodiments, the glass article comprisespost-ion exchanged glass. According to some embodiments, the defectlines extend the full thickness of the at least one inner contour edge.According to at least some embodiments, the at least one edge surfacehas an Ra surface roughness less than about 0.5 micrometers afterremoval of a part from substrate 10. According to at least someembodiments, the at least one edge has sub-surface damage up to a depthless than or equal to about 75 micrometers.

The foregoing process yields a consistent edge. This results in edgestrength, as measured by a 4-pt bend test, with a tight distribution.For a non-chemically strengthened glass like Corning Eagle XG®, theresulting edge strength can have an average value greater than about 90MPa, with a standard deviation typically less than about 15 MPa.Furthermore, since the defect lines are generally made symmetricallythrough the full body of the substrate, the edge strength will generallybe close to identical (within 10%) whether or not the top or bottomsurface of the part is placed in tension during the strength testing. Adifference between the strength distribution from one major surface tothe opposite major surface (depending on the direction of bend) is lessthan 10% of the mean strength distribution. The edge surfaces exhibit nochipping with a size greater than about 50 micrometers in lateral extentevaluated by examining a region of 500 micrometers in width along thefull perimeter of the inner and outer edge surfaces.

Articles produced by the foregoing process exhibit low warp, as can beseen by FIG. 14. FIG. 14 shows the warp (flatness) data of 95 millimeterouter diameter annuli (26 mm inner diameter) taken at different lateralpoints across a fusion drawn glass substrate. The annuli were cut from100×100 millimeter segments of the substrate that were measured forflatness before laser cutting into annuli (FIG. 14A). After lasercutting into annuli, the flatness of each disk was re-measured (FIG.14B). The data of FIG. 14B indicate the flatness of each final annulusas a function of its original spatial location in the fusion draw sheet.These data indicate that the laser-cut annuli maintained flatness equalto or less than about 15 micrometers. Comparison with the originalflatness data also indicates the flatness of each annulus agreed wellwith the flatness of the 100×100 millimeter cut squares. Articlesproduced by methods disclosed herein can have a total thicknessvariation (difference between maximum and minimum thickness) equal to orless than about 10 micrometers. Flatness (warp) was measured using aNEXIV VMR 3020 coordinate measuring system available from Nikon® andemploying MountainsMap® analysis software by Digital Surf.

Articles produced by the foregoing processes may comprise equal to orless than about 5 MPa internal residual stress, and in some embodimentsequal to or less than about 0.5 MPa residual stress.

Annuli produced by methods disclosed herein can have a concentricity(evaluated as the distance between the centers of the inner and theouter perimeters of the annuli) equal to or less than about 15micrometers, for example in a range from about 0 micrometers to about 12micrometers, in a range from about 0 micrometer to about 10 micrometers,in a range from about 0 micrometers to about 5 micrometers, and in someembodiments in a range from about 2 micrometers to about 6 micrometers.Outer diameters of the annulus can be within +/−12 micrometer of thenominal diameter. Concentricity was measured using a NEXIV VMR 3020coordinate measuring system, available from Nikon® and employingMountainsMap® analysis software by Digital Surf.

In the instance where the article is a platter for a hard drive device,for example, the article may undergo additional processing. For example,the edge surfaces of the article may be ground and/or polished to thedrive manufacturer's specifications. The edges of the annulus mayadditionally be beveled. In some embodiments, the major surfaces 40, 42of the glass substrate may be ground and/or polished. In such instance,a total of no more than about 0.1 mm of glass need be removed from themajor surfaces of the glass article after removal of the article fromthe surrounding substrate. Additionally, the annulus may be coated as iscustomary for a hard drive platter. For example, the annulus may becoated with a coating of magnetic media.

In some embodiments it may be desirable to ion exchange the glasssubstrate. In such instances, it is preferably that the ion-exchangeprocess be performed prior to the cutting processes.

Example

A Corning Lotus NXT glass substrate 0.7 mm thick was positioned on apolymer support substrate, the support substrate comprising a pluralityof recesses, each recess having a 30 millimeter diameter and a 2millimeter depth. The substrate was held in place by a series of throughholes in the polymer substrate and a vacuum was applied to the throughholes. A plurality of defects were formed along a plurality of firstcircular paths and a plurality of second circular paths concentric withthe first closed paths using a Coherent Hyperrapid Picosecond laseroperating at 29 watts, with a pulse width of about 9 picoseconds, apulse frequency of 100 kHz, and operating in a burst mode with 5 pulsesper burst. The line focus diameter was approximately 2 micrometers(FWHM), with a length of 1.2 millimeters. The laser was traversed at aspeed of 12 meters/minute to produce defect lines spaced 4 micrometersapart along each of the first and second closed paths. Radii of thefirst closed paths were 25 millimeters and radii of the second closedpaths were 95 millimeters. The first and second closed paths defined aplurality of annuli. The plurality of first closed paths defined aplurality of plugs.

Upon completion of the defect forming stage, the first and second closedpaths were traced using a 200 watt Synrad CW laser operating at 170watts, defocused to a 7 millimeter beam diameter at the glass surface,wherein the laser beam was traversed at about 12 meters/minute to jointhe defect lines along each of the first and second paths with a crack,thereby isolating the annuli from the glass substrate and the plugs fromthe disc defined by the second circular paths.

The plugs were then heated using the same Synrad CW CO₂ laser operatingat 200 watts and adjusted to produce a defocused 6 millimeter diameterlaser beam at the glass surface. This laser beam traced a 10 millimeterdiameter circle four times within approximately 4 seconds. The plugswere allowed to cool passively (without active cooling), whereupon theplugs dropped from the glass discs within about 25 seconds after thebeginning of cooling (at the cessation of heating).

While exemplary embodiments have been disclosed herein, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the scope of theinvention encompassed by the appended claims.

What is claimed is:
 1. A glass article comprising: a first majorsurface; a second major surface opposite the first major surface; acircular inner perimeter; a circular outer perimeter concentric with theinner perimeter, the inner perimeter and the outer perimeter defining anannulus therebetween, a thickness extending between first and secondmajor surfaces equal to or less than about 1 millimeter, a firstunground and unpolished edge surface between the first and second majorsurfaces and extending around the inner perimeter and a second ungroundand unpolished edge surface between the first and second major surfacesand extending around the outer perimeter; and wherein an R_(a) surfaceroughness of at least one of the first or second edge surfaces is equalto or less than about 0.5 micrometers.
 2. The glass article according toclaim 1, wherein at least one of the first or second edge surfacescomprises a plurality of defect lines extending orthogonally between thefirst and second major surfaces, and wherein a diameter of each defectline is less than or equal to about 5 micrometers.
 3. The glass articleaccording to claim 1, wherein a depth of subsurface damage along eitherone of the first or second edge surfaces is equal to or less than about75 micrometers.
 4. The glass article according to claim 3, wherein thedepth of subsurface damage is equal to or less than about 25micrometers.
 5. The glass article according to claim 1, wherein a warpof the glass article is equal to or less than about 50 micrometers. 6.The glass article according to claim 5, wherein the warp is equal to orless than about 15 micrometers.
 7. The glass article according to claim1, wherein an anneal point of the glass article is equal to or greaterthan about 700° C.
 8. The glass article according to claim 7, whereinthe anneal point of the glass article is equal to or greater than about800° C.
 9. The glass article according to claim 1, wherein a compactionof the glass article after exposure to a temperature of 600° C. for aperiod of 30 minutes, upon cooling to a temperature of 23° C., is equalto or less than about 35 ppm.
 10. The glass article according to claim1, wherein the compaction is equal to or less than about 20 ppm.
 11. Theglass article according to claim 1, wherein the glass article comprisesequal to or less than 5 MPa internal residual stress.
 12. The glassarticle according to claim 1, wherein the glass article is a chemicallystrengthened glass.
 13. The glass article according to claim 1, whereinan average roughness R_(a) of either one of the first or second majorsurfaces is less than about 1 nanometer.
 14. The glass article accordingto claim 13, wherein the average roughness R_(a) of either one of thefirst or second major surfaces is less than about 0.5 nanometers. 15.The glass article according to claim 1, wherein the glass articlecomprises equal to or less than about 0.5 wt. %, SnO₂.
 16. The glassarticle according to claim 1, wherein the glass article comprises equalto or less than about 0.15 wt. % SnO₂.
 17. The glass article accordingto claim 1, wherein a distance between adjacent defect lines of theplurality of defect lines is equal to or less than about 7 micrometers.18. The glass article according to claim 1, wherein the glass articlecomprises less than or equal to 0.1% of an alkali metal oxide.
 19. Theglass article according to claim 1, wherein the first and second majorsurfaces are unground and unpolished.
 20. The glass article according toclaim 1, wherein the first and second major surfaces are free of anycoating.
 21. The glass article according to claim 1, wherein a diameterof the circular outer perimeter is within +/−15 micrometers of apredetermined nominal circular outer diameter.
 22. The glass articleaccording to claim 21, wherein the diameter of the circular outerperimeter is within +/−10 micrometers of the predetermined nominalcircular outer diameter.
 23. The glass article according to claim 1,wherein a diameter of the circular inner perimeter is within +/−25micrometers of a predetermined nominal circular inner diameter.
 24. Theglass article according to claim 23, wherein the diameter of thecircular inner perimeter is within +/−10 micrometers of thepredetermined nominal circular inner diameter.
 25. The glass articleaccording to claim 1, wherein a center of the inner circular perimeterand a center of the outer circular perimeter are displaced from eachother by no more than about 10 micrometers.
 26. The glass articleaccording to claim 25, wherein the center of the inner circularperimeter and the center of the outer circular perimeter are displacedfrom each other by no more than about 5 micrometers.